kaolinite - teaching student specimens of the primary constituent of kaolin clay, hard vitreous form - Unit of 5 specimens
kaolinite Al4(Si4O10)(OH)8 Unit of 5 student specimens
Kaolinite is the primary constituent of kaolin clay. Its physical structure is like a sandwich, with aluminum hydroxide layers, called gibbsite layers, bonded to silicate sheets. These sheets are electrically neutral, so they are bonded by very weak van de Waals forces, easily sliding apart to give kaolinite its softness and greasy feel. It has a similar structure to minerals in the serpentine group.
Rocks with a silica-rich composition that contain aluminosilicate minerals weather to clays. This kaolinite was formed by the hydrothermal alteration of Pleistocene lacustrine sandstone and the underlying rhyolite. The sandstone was derived from granitic rocks, which contain abundant feldspar and after hydrothermal alteration or weathering are a common source for kaolinite.
When the vitreous form of magnesite was first discovered in Muddy Valley, Nevada in the late 1800s, it was thought to be kaolin and plans were made to mine it as such. In 1915, before mining could begin, a specimen sent to the U.S. Geological Survey was identified as magnesite. X-ray diffraction confirms the identification of this material as kaolin.
Because kaolinite does not absorb water, it does not expand when it comes in contact with water and is the preferred type of clay for the ceramics industry. It is also used as a filler in rubber and in paper, paint, plastics and cosmetics.
This kaolinite comes from the inactive Huntley Kaolinite Mine in Mono County, California.
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